This article was first broadcast in Episode Two Hundred and Forty Nine on 10th October, 2023.
Note: This article was adapted from an episode script, and so there may be parts that don’t flow well when read, because they were initially designed for broadcast.
A few different classes in D&D eventually progress to the point where they become totally immune to diseases, and it’s often part of a level bonus, where that’s the primary thing they receive for reaching that milestone.
However, many people see that and wonder if it’s actually a bonus at all. For most people playing, diseases are not a factor in most of their adventures. They might come across a sick child in need of help or a plague-ridden town, but rarely does the adventure or the DM running it do things like have characters save vs catching whatever ailment the NPCs have. So what’s the point of the immunity then?
Despite the scarcity, there are a few places disease actually shows up in 5th edition. The two primary sources are monsters and spells.
We’ll get the spells out of the way first because the list is shorter. Of the more than 500 spells currently present in 5th edition, a grand total of 6 deal with disease. Detect Poison and Disease is an obvious one, and if you need us to explain what the spell does, we have a suggestion for your next ability score increase. Purify Food and Drink removes diseases from anything you or anyone else is about to eat, and Lesser Restoration is how you get rid of a disease if you’ve already caught it, unless you want to bring out the big guns and use Heal.
However, unlike in real life, finding and getting rid of the diseases in D&D is a lot easier than causing them. Contagion and Harm are the two spells in 5th edition that inflict diseases. Where all of the healing and detections spells mentioned were level 2 and lower, Contagion is a 5th level spell and Harm is 6th. Both of them explicitly say that the damage they inflict is due to the creation of a disease.
The other main way to contract a disease in 5e is from a creature. There are actually a number of creatures that do it, too. First you have the obvious sources like the literal Diseased giant rat, Swarm of Maggots, and everyone’s favorite living garbage disposal, the Otyugh.
Demons are another common source for disease infliction, the Bulezau [ˈbuːlɛzaʊ] being a prime example, as are any demons that ally with, or are created by, Zuggtmoy.
Now on to what we are getting at here. For most of these creatures, the mechanical effect of the disease just inflicts the poisoned condition, at least immediately. So anything that’s immune to being poisoned, which is a lot of things in 5e if you recall, isn’t going to show obvious signs that they’ve contracted your average disease. The only other effect of most diseases in this edition are the requirement that the creature make a save after each long rest. If they fail, they lose a number of hit points from their hit point total, dying if they reach 0. However, the number of hit points lost is often a d4 and they return when the disease is cured. For anyone over 3rd level or so that whole thing would be an inconvenience at best.
There are a few specific diseases that behave differently, but they’re very unique to the creatures that inflict them.
Some of the demonic diseases don’t inflict ongoing damage, but if a creature dies while they’re infected, they turn into a demon, which kind of precludes any resurrection or anything like that. However, if they don’t fail their death saves, there’s no other effect.
Red Slaadi spread diseases with their claws that, if left untreated for three months, eventually result in the host dying as a slaad bursts from their body, Blue Slaadi inflict Chaos Phage, which is scarier; the infected can’t regain hit points and they lose 3d6 HP from their total each day. If or when they die, they transmute into a Slaad.
Aboleths inflict an infection that forces a creature’s body to conform to living underwater and it’s very hard to get rid of; if a creature’s succumbed, a Heal spell is the only thing that will do it.
Many of the aforementioned demon lord’s minions spread an infliction called the Spores of Zuggtmoy. That infection causes the victims to go mad for a period of three days, after which the spores spread through the body and the creature turns into a myconid devoted to the demon lord.
All of that taken together sort of highlights the issue with diseases in 5e. For the average adventuring party, they just don’t have that much impact.
Because all of them are classified as diseases, that means Lesser Restoration takes care of it, and all of them have a multi-day timeframe to fix. Most Clerics or Druids will end up with a 2nd level spell slot to spare unless it’s been a really trying day, and even if they don’t, putting it off until morning isn’t risking much for probably the first couple of days. A barbarian or a fighter catching a disease can probably go a full week before they really have to start worrying about anything.
That’s obviously not the case with the more exotic diseases, but in most cases the characters will be able to see that coming, or can figure it out after a short time. Someone inflicted with Chaos phage or Spores of Zuggtmoy definitely will seek help, and the Aboleth infection is a bit of a nightmare, but so are Aboleths, so that fits. On the other hand, the Red Slaad egg takes longer to gestate than the timeframe of most campaigns, so all that disease means is one character is going to have a much darker epilogue than their buddies.
In short, unless the characters are fighting very specific and pretty exotic enemies, a disease isn’t going to have much impact on their regular adventuring.
Given all that, it’s not hard to see why Wizards of the Coast is considering doing away with diseases entirely for One D&D. But they weren’t always easily ignored, minor inconveniences that a lot of people were immune to or that came from really exotic creatures or locations.
Back in 4th edition, there was more variety and more complexity to diseases. Many of them could be picked up just from walking around and, once contracted, they had an immediate effect. Then after each long rest, the afflicted character would make what we today call a Constitution save. There were two targets. If they rolled the highest target, the symptoms got better. If they hit the middle target, they were no worse off, but if they missed that, the disease got worse. If the disease got bad enough, it inflicted a permanent penalty that could only be cured with magic or a potion to remove a disease. If they even survived.
As an example, there’s one called blinding sickness. If a character caught it, the first effect was that they lost a hit die. If they recovered they were fine, but if it got worse, they got blurred vision, meaning any creature more than 10 feet away counted as being concealed for them. If they got worse from there, they were blind until someone healed them of the disease.
Compare that to something called Mummy Rot. As soon as the character is infected, any healing done to them is only half as effective. If the disease gets worse, they start their day taking 10 necrotic damage that can’t be healed. If the disease isn’t cured before it gets worse, the character dies.
Magical healing wasn’t that much rarer in 4th edition, but the point is that the diseases very often couldn’t be put off or ignored. If someone caught something like the blinding sickness, and didn’t have a good Con save, they were very quickly going to become less effective in combat. If it was something worse like Mummy Rot, not only would they be at serious risk of dying from failed saves, but keeping them alive in combat got a lot harder immediately.
If you want things to get scarier, go back to 3rd edition, or 3.5. The diseases in that edition functioned basically the same way as they do in 5th; you contract the disease, you take some damage, and then after a long rest if you don’t get better you roll a d4. The difference is, that d4 didn’t subtract from your HP total; it subtracted from a stat. So suddenly you wake up in the morning and the Wizard’s gone from INT 20 to INT 16, and they’re at risk of joining the Barbarian for some beers and offensive womanizing unless the cleric gets their act together. What stat was targeted depended on the specific disease.
If for whatever reason you want disease to be something the characters have to actually respond to and not put off like that odd insect bite you found on your hand when you woke up, it might be worth looking back at the earlier editions. All of the scary diseases from 5th edition are, as mentioned, really specific to particular monsters.
The 3rd edition diseases are the easiest to port over, though as mentioned they will be very scary for a lot of players; there is almost nothing in 5e that interferes with a character’s stats in the long term, and it might cause genuine panic if the Barbarian suddenly has a strength below 18.
There is a little more variety and complexity to the 4th edition diseases, which also means more work to convert them. Some of the diseases affect mechanics or have triggers that aren’t valid in 5e (such as “when a target is bloodied,” which meant when they drop below half HP). Also the save DCs for the tracks would have to be completely redone since bounded accuracy wasn’t a thing, so DCs in the low 30s weren’t impossible targets, they just meant the characters had to be at the right levels. If you want to completely homebrew it, you can just steal the “disease track” mechanic and fill in custom values yourself.
So diseases may not be a big deal in 5th edition, but if you really need some virulent plague or rampant infection that characters would have to actually pay attention to, and you don’t want a plot centered around an extraplanar invasion, you can make it work with a little effort.